There has been widely known a horizontal bag-making/packing/ packaging machine in which, while packaging articles are successively fed into a packaging material such as, for example, a film and the like being fed out horizontally into the form of a tube through means of a bag-making device, the longitudinal end portions of the tubular packaging material containing the packaging articles are subjected to lengthwise sealing of the overlapping faces thereof, followed by crosswise sealing and cutting of the tubular packaging material upon both sides of each packaging article so as to successively produce oblong pillow type packages. In this connection, the above longitudinal sealing is generally referred to as "center sealing"; whereas the crosswise sealing is generally referred to as "end sealing", and these latter mentioned terms will be used hereinafter, respectively.
The horizontal bag-making/packing/packaging machine mentioned above has various types of working mechanisms such as, for example, a conveyor for feeding packaging articles, feed rolls for delivering a packaging material, rolls for achieving center-sealing, sealers for achieving end-sealing for the packaging material, and others. The driving system of the conventional packaging machine described above has one main motor as a common driving source and is designed to drive a plurality of the working mechanisms mentioned above in connection with one another through means of mechanical power transmission systems, respectively, using this motor.
The feeding of the packaging articles to the above bagmaking /packing/packaging machine is generally achieved by forwarding them at a predetermined speed as a result of being engaged with an endless chain of the above conveyor having engagement attachments which are disposed thereon with a predetermined spacing defined therebetween. Accordingly, if it should happen that packaging articles are not supplied to any one of the corresponding attachments of the conveyor for some reason, then feeding of the packaging articles to the tubular packaging material formed within the packaging machine is temporarily interrupted so as to result in an absence of a packaging article (there may also be considered a case when such absence occurs separately and when two or more absences occur in succession). If such an absence of a packaging article should occur, a "vacant package" containing no packaging article will be present among the intact packages to be successively formed by means of the packaging machine. The formation of such vacant packages will not only lead to a waste of the packaging material but also involves inconveniences in that a special device for separating and removing them from among the intact packages is required. Therefore, when there is any absence of a packaging article within the row of the packaging articles transported upon the conveyor, it is necessary to institute procedures for preventing the formation of such vacant packages.
Accordingly, within a conventional packaging machine having a purely mechanical construction, procedures are used to detect the absence of a packaging article by means of a photoelectric tube and the like within the row of the packaging articles fed with a predetermined spacing therebetween upon the feed conveyor and for stopping the film delivering mechanism and the endsealing mechanism based upon such detection. For example, as disclosed in Japanese Utility Model Publication No. 10277/1975, there has been employed a system wherein a detection section for detecting the absence of packaging articles is disposed within the feed path of the feed conveyor; and a clutch which is actuated by means of a signal from this detection section is disposed for the respective driving sections of the packaging sheet delivering mechanism and the rotary sealing mechanism, so that the packaging sheet delivering mechanism and the rotary sealing mechanism may be stopped by actuation of the clutches during the absence of packaging articles upon the feed conveyor.
However, in the packaging machine having the above construction, substantial mechanical shock will be produced when the packaging sheet delivering mechanism and the rotary sealing mechanism are stopped or started as a result of the actuation of clutches, and furthermore, the system suffers from the problem that it does not exhibit a high-speed response upon detection of any absence of a packaging article.